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420                                ALASKAN GLACIER STUDIES
Observations by the National Geographic Society's Expeditions. Our own studies of Miles Glacier were made by both authors in August, 1909, and by the junior author in August and September, 1910, and in June, 1911. The first set of observations1 was limited to parts of two days, while those in 1910 a occupied parts of two weeks, during which we made detailed studies and took many photographs, while Mr. Lewis made the topographic map reproduced as Map 9 (in pocket). The study of Miles Glacier in 1911 occupied only a few days, dealing chiefly with conditions of former glaciation rather than with Miles Glacier itself.
The Miles, a Bulb Glacier—General Conditions. Miles Glacier is an excellent example of a bulb glacier, a class intermediate between the valley glaciers and the piedmont glaciers. Miles Glacier is a bulb glacier which, on emerging from its mountain valley into the flatter grade of the broad Copper River valley, spreads out in a bulb or fan (Map 9). The valley glacier and the bulb will be discussed separately.
The Valley Glacier. The valley glacier (Fig. 61) appears to be perfectly normal. It has severely crevassed white ice with rather broad lateral moraines in which the ice is little crevassed. Its mountain walls (Fig. 6£) rise to heights of 2300 to 4900 feet, with slopes at the rate of three to six thousand feet to the mile. The number of tributary

FIG. 62.   NATURAL SOALH CROSS-SUCTION OF MTT.BB GLA.CIHR IN ITS MOUNTAIN VALLEY.
ice streams is unknown, but there are two prominent ones entering the main glacier from the south, four and nine miles respectively, from the terminus, and another large one coming in from the northeast ten miles from the end. This tributary ice tongue, Van Cleve Glacier,8 is over a mile wide and enters the main glacier at an elevation of 1800 feet above sea level.
The surface of the main valley glacier slopes at the rate of less than 150 feet to the mile, but three miles from the terminus, the slope steepens to 178 feet per mile, and just before reaching the ice precipice, in the lake, the slope increases to 660 feet per mile, as if Miles Glacier valley had a hanging relationship to the main Copper River valley.
The Ice Cliff. The portion of the ice front which discharges bergs into Miles Lake is essentially the terminus of the valley glacier (PL CLIX). The southern edge is exactly at the mouth of the valley, for this part of the glacier does not spread out beyond
i Tarr, R. S. and Martin, Lawrence, Nat. Geog. Mag., Vol. XXI, 1910, pp. 13-14, 23, 37.
> Martin, Lawrence, Nat. Geog. Mag., Vol. XXTT, 1911, pp. 542-548; in H. F. Reid's Variations of Glaciers for 1910, Journ. Geol., Vol. XIX, 1911, p. 458; Zeitachrift fUr Gletscherkunde, Band VI, 1911, p. 102; Mastering the Alaskan Glacier Barriers, Scientific American Supplement, Vol. T.yyT, 1911, pp. 305-807; Peter-manns Geog. Mitteilungen, Jahrgang 1912, Septemberheft, Tafel 9.
« Named in 1910, for J. R. Van Cleve, General Manager of the Copper River and Northwestern Railway.